The importance of SO_2 and SO_3 for sulphation of gaseous KCl - An experimental investigation in a biomass fired CFB boiler

摘要

This paper is based on results obtained during co-combustion of wood pellets and straw in a 12 MW circulating fluidised bed (CFB) boiler. Elemental sulphur (S) and ammonium sulphate ((NH_4)_2SO_4) were used as additives to convert the alkali chlorides (mainly KG) to less corrosive alkali sulphates. Their performance was then evaluated using several measurement tools including, IACM (on-line measurements of gaseous alkali chlorides), a low-pressure impactor (particle size distribution and chemical composition of extracted fly ash particles), and deposit probes (chemical composition in deposits collected). The importance of the presence of either SO_2 or SO_3 for gas phase sulphation of KCl is also discussed. Ammonium sulphate performed significantly better than elemental sulphur. A more efficient sulphation of gaseous KCl was achieved with (NH_4)_2SO_4 even when the S/Cl molar ratio was less than half compared to sulphur. Thus the presence of gaseous SO_3 is of greater importance than that of SO_2 for the sulphation of gaseous KCl.